115 Yamaha alarm on

[truckrunner9]

Well about 1 month ago i had started trying to figure out what could make my motor alarm come on i have changed the water pump the thermistats,temp sencers.It still comes on if you get over 4000 rpm's.Im about to clean the carbs to see if maybe one of the carbs are leaning out one cylender. This fuel with Meth added i under stand it is giving he rubber hoses trouble.So im goning to check out the hoses. If any one has an idea pleasae comment.

[99yam40]

Need to make sure it is a temp alarm.

Might use a temp gun to measure the head temps to see if one spot is high enough to set off alarm when alarm is sounding.
Or disconnect temp switches one at a time while alarm is sounding to see which one if any of them is sounding the alarm.

If it is a true temp alarm, then you may need to pull heads to clean all passages.

[Sequoiha]

if it is coming on at 4000 rpms and runs ok at lower rpm, you have a stuck closed pressure control valve.. Poppit valve,, check it out and get back with your result..

[rodbolt17]

pressure control valve wont affect temp at 4000 RPM, by that time it can be removed,plugged off or whatever.
if it were stuck closed cooling water pressure would probably exceed 30 PSI which would/could lead to gasket sealing issues.
typically what your describing,if its an actual temp alarm and not oil.
is either a head gasket leaking combustion gas into the cooling system or scale buildup in the cooling passages.
either requires head and water cover jacket removal.

[truckrunner9]

Pressure control

I have cleaned the carbs and changed the pressure control valve and it still does the same thing.I guess the next thing is to pull the heads and clean the passages.THank you all for the help.I'll get back with the results. List of what i have done so far 1changed heat sensers,water pump ,thermastates pressure con***** valve .Thank you'll for your thoughts really helping me alot by the time i get this figured out it should be in top condition once again.Oh and i had removed the oil injection 2 years ago and mix my own and unpluged the harnest so its not oil.Thank you once again.

[99yam40]

why did you modify the oil?

Did you pull the oil pump drive shaft?

wiring shorting could be a problem still, but do not see how RPM would affect that.

But I would still measure temps to figure out what is getting hot before going too far

[Sequoiha]

pressure control valve wont affect temp at 4000 RPM, by that time it can be removed,plugged off or whatever..

are you serious, i run into this all the time, there is not enough water flow through the thermostats at a higher rpm to cool the engine, if the valve is stuck closed it will over heat at higher rpms. ( test it and get back with the results.) if it is stuck open it will over heat at idle because the block will not fill up with water. I am in a saltwater enviroment and this is a common occurance.

[rodbolt17]

appearently you dont understand the water flow on that V4.
water enters under the powerhead and is channelled up both sides of the block AND the water cover for the exhaust, any unused water(as the valve is opened) is dumped DIRECTLY into the EX water stream and blown out the prop boss.
if stuck shut it will make more than 30 PSI which may cause a gasket leak but wont cause overheat.
typically we see them partilly stuck open which DUMPS water pressure and typically shows up at low engine speeds.
infact on of the local yamaha hoyrodders in this are actually blocks off the pressure valve and modifys the T stat housing to force water pressures above 28 PSI.

water under pressure has a higher boiling point than at standard air pressure.
means it can absorb more heat before boiling in the cooling passages and causing steam hot pockets.
hot water from the block is dumped out the heads viathe t-stats via the covers and into the ex stream.
the 3.1 and 3.3 engines are a bit different but the V4 and 2.6L v6 share the same cooling water path.
if stuck shut at high speeds it will cause more wear on the hub/key and rob some horsepower but not overheat.
v6 merc yes,v4 yamaha no.
that hose that goes FROM the pressure control discharge TO the powerhead adapter simply dumps excess water directly into the ex water stream.
it also aides in cooling the tuner and midsection area some.
the yamaha water pump is a two stage pump.
positive displacement at low speeds changing to a centrifical pump at high speeds.
in order to maintain decent pressure at low crank speeds yet not overpressuring and creating issues at higher speeds is the only reason why its there.
most 2.6l v6 and v4 2 strokes tend to run 3-5 PSI at low speed increasing to 15-20 psi at or near WOT.
excess water is simply dumped.

[Sequoiha]

Thanks for the lesson king rodbolt, apparently ive been misdiagnosing and wasting my customers money for many years,, sure am glad we have people like you on these forums to keep us straight. and by the way if i didnt understand the question or the product i would not have offered my input.

no need to degrade me, just answer the op question to the best of your ability and ill do the same, let him make the decision of what repair or course of action to take.

nothing else to say on this subject.

[99yam40]

I can understand what Rodbolt17 posted about the subject, and it makes sense to me
I have seen you post this as a cause for high speed overheat before and mentioned I did not think it was correct but did not have enough personal info on the water flow at the time,
Sorry but I still have not been able to figure out your reasoning on how the stuck closed PRV would cause high RPM overheat, as it would force even more water through motor instead of dumping it before going through the motor.

I do believe in changing the water pump, Inspecting/replacing PRV, and measuring head/ block temps and replacing/ testing stats and temp sensors/switches each and every time there is an overheating problem to keep from having the motor returning repeatedly for same problem.

I would not say you are wasting time and money changing them, I just do not understand the reasoning behind it causing high RPM overheat

I do appreciate all who post their thoughts and info on this web site helping others with their problems

[midgiegualla]

So when the PRV opens does it dump cold water straight from the pump ?? Or does it dump warm water from the engine ?? Just interested in this discussion !!!

[99yam40]

the 3.1 and 3.3 engines are a bit different but the V4 and 2.6L v6 share the same cooling water path.
if stuck shut at high speeds it will cause more wear on the hub/key and rob some horsepower but not overheat.
v6 merc yes,v4 yamaha no.
that hose that goes FROM the pressure control discharge TO the powerhead adapter simply dumps excess water directly into the ex water stream.
it also aides in cooling the tuner and midsection area some.

Seems different motors do it differently

[rodbolt17]

as far as the PRV valve, all V 2 stroke engines simply dump excess water down the ex around the tuner and out the prop.
next time you have the ex cover boff look at the relation of the tell tale outlet and the PRV outlet.
next time you have a powerhead off simply spray water down the RRV to adapter hose.
its a very simple highly misunderstood pressure control system.
as engine speed increases the pump goes from a positive displacement to a centrifical pump.

the vanes actually pull away from the insert.

as pressure increases so does the HP required to make it.

comes a point its a waste of time.
to much HP loss and wear on the hub and drive key.
thats the whole function of a pressure con*****ed system.
sorry, no black magic or voodoo.

next we will hear about why not to turn the waterv full on when flushing.
another myth,kinda like not running the fuel tank low, from 70 years ago.

dont mean to bust anyones chops.
but I have done this a long long time.
and yes >I have sprayed water down the PRV discharge hose while watching where it goes with the gear case off.
years ago when you went to jap motor schools,tohatsu,yamaha,suzuki, if you had a stumper question the answer was always, why you need to know.